1. Field of the Invention
The present invention relates to a method of using, in a topical cosmetic composition, or for the manufacture of a topical dermatological composition, at least one compound comprising a phenyloxime fragment depigmenting and/or bleaching human skin, body hair or head hair.
2. Description of the Background
The color of human skin depends on various factors and in particular on the seasons of the year, race and sex, and it is mainly determined by the nature and concentration of melanin produced by the melanocytes. Melanocytes are specialized cells which synthesize melanin, via specific organelles, the melanosomes. In addition, at various periods in their life, certain individuals develop darker and/or more colored marks on the skin, and more especially on the hands, making the skin non-uniform. These marks are also due to a large concentration of melanin in the keratinocytes located at the surface of the skin.
Similarly, the color of body hair and head hair is due to melanin, and when the body hair or head hair is dark, certain individuals wish to make them lighter. This is particularly advantageous for body hair which is less visible when it is light than when it is dark.
The substances most commonly used as depigmenting agents are, more particularly, hydroquinone and its derivatives, in particular its ethers such as hydroquinone monomethyl ether and monoethyl ether. Unfortunately, although these compounds have a certain level of efficacy, they are not free of side effects on account of their toxicity, which can make them problematic or even hazardous to use. This toxicity arises from the fact that they intervene in fundamental mechanisms of melanogenesis by killing cells which then create the risk of disrupting their biological environment and consequently oblige the skin to remove them by producing toxins.
Thus, hydroquinone is a compound which is particularly irritant and cytotoxic to melanocytes, and its total or partial replacement has been envisaged by many authors.
The use of harmless topical depigmenting substances which have good efficacy is most particularly desired in order to treat regional hyperpigmentations caused by melanocyte hyperactivity, such as idiopathic melasmas occurring during pregnancy ("pregnancy mask" or chloasma) or during oestro-progestative contraception, localized hyperpigmentations caused by hyperactivity and proliferation of benign melanocytes, such as senile pigmentation marks known as actinic lentigo, accidental hyperpigmentations or depigmentations, which may be due to light-sensitization or to post-lesional cicatrization, as well as certain leukodermias, such as vitiligo. For the latter pigmentation conditions (it being possible for cicatrizations to result in a scar giving the skin a whiter appearance, and leukodermias), failing the ability to repigment the damaged skin, the approach finally adopted is to depigment the regions of residual normal skin in order to give the skin as a whole a uniform white shade.
Thus, a need exists for a novel agent for bleaching human skin, body hair and/or head hair, which acts as effectively as the known agents but does not have their drawbacks, i.e. which is non-irritant, non-toxic and/or non-allergenic to the skin and is stable in a composition.